1. Field of the Invention
This invention relates to a non-autocross-linking binder composition for use in water dilutable lacquers which are capable of being deposited electrophoretically and to aqueous electro dip lacquer coating compounds (ATL or KTL baths) capable of being deposited at the anode or cathode. This invention also relates to methods using the lacquer coating compounds containing the non-auto-cross-linking binder composition in coating articles.
2. Description of the Related Art
Electrode dip lacquer coating compounds are used as primers on a large technical scale. They are also referred to as electrophoresis lacquers or EC lacquers. Maleate oils, butadiene oils containing carboxyl groups or epoxide resins containing amino groups are frequently used as EC lacquers. Thermal cross-linking of these binders is carried out by various processes, e.g. by the reaction of unsaturated double bonds or functional groups of the principal resin with formaldehyde condensation resins, blocked polyisocyanates or transesterifiable cross-linking agents. Such lacquers, while useful, often do not necessarily have all the desired properties for a particular customer's specific requirements.
For the formation of lacquers which are stable in color, of the kind required, for example, for the manufacture of domestic implements, these systems have the undesirable property of severe yellowing. When the lacquer is applied in two coats, bloom-like color changes may even occur in the top coat, which impair the surface appearance of the lacquer. Other binder systems known in the art based on poly(meth)acrylate resins which have less tendency to undergo yellowing have not hitherto shown the high protection against corrosion obtainable with amino epoxy resins in the motor car industry. Aqueous, non-yellowing electro dip lacquer coating compounds containing, as a principal resin, a synthetic resin binder containing primary and/or secondary hydroxyl groups and primary, secondary and/or tertiary amino groups, such as amino poly(meth)acrylate resins having a hydroxyl number of from 80 to 250 (mg KOH per g of solid resin), an amine number of from 30 to 150 (mg KOH per g of solid resin) and an average molecular weight (Mn) of from 250 to 10,000 are described in DE-A-No. 34 36 346 (EP No. 180051).
In DE-OS No. 23 57 152 there are described aqueous, non-yellowing electrode dip lacquer coating compounds containing, as a principal resin, poly(meth)acrylate resins containing primary and/or secondary hydroxyl groups and carboxyl groups and composed of
20 to 60% by weight of hard monomers, PA1 20 to 40% by weight of soft monomers, PA1 4 to 20% by weight of monomers containing hydroxyl groups and PA1 4 to 20% by weight of .alpha.,.beta.-unsaturated carboxylic acids. PA1 (a) 80-95% by weight of a copolymer of PA1 (b) 5 to 20% by weight of a polyisocyanate containing unmasked isocyanate groups: and, PA1 (a1) 0.5 to 40% by weight of N,N-di-C.sub.1-4 -alkyl amino-C.sub.1-8 -alkyl(meth)acrylamides and/or a mixture of N,N-di-C.sub.1-4 -alkylamino-C.sub.1-8 alkyl(meth)acrylates and N-substituted (meth)acrylamides and/or (meth)acrylamide in which the ratio of amino(meth)acrylates to amido(meth)acrylates should be in the range of from 1:2 to 2:1, PA1 (a2) 10 to 40% by weight of hydroxy-C.sub.2-8 alkyl(meth)-acrylates. PA1 (a3) 20 to 89.5% by weight of copolymerizable .alpha.,.beta.-olefinically unsaturated compounds and
Both these resin systems have the disadvantage of having insufficient pigment absorption capacity and providing insufficient protection against corrosion, especially at the edges and corners of coated articles.